SUPPLEMENT: Rest Activity Rhythms and Cognitive Function in Stable Heart Failure Abstract We are submitting this application in response to NOT-AG-18-039. Our scientific premise is that disruptions in circadian rhythmicity (CR) and sleep contribute to cognitive impairment (CI) in adults with chronic heart failure (HF) who are at especially high risk for cognitive impairment and dementia. The purpose of this longitudinal study is to improve understanding of the contributions of the rest activity rhythm (RAR) to cognitive function among HF patients. This information is needed to guide possible future interventions focused on these modifiable factors to prevent CI or reduce its progression. We will address the following specific aims: 1) characterize changes in cognitive function (cognitive ability and vigilant attention) over one year among adults with stable HF and insomnia; and 2) examine the extent to which the RAR and characteristics of sleep (insomnia severity, self-reported sleep quality, actigraph-recorded sleep duration and efficiency), collected at baseline and 4 additional time periods over one year, independently or together predict cognitive function at one year. Our hypothesis is that a more stable (inter-daily stability), consistent (intra-daily variability) and robust (circadian coefficient) RAR, lower levels of insomnia severity, and higher sleep efficiency and duration will predict better cognitive function at one year. We will also explore the associations of variations in light levels to the RAR and cognitive function and the extent to which there are interactions between light, sleep characteristics, the RAR and cognitive function. Recruitment and data collection/analysis are underway in the parent study, an ongoing 5-year randomized controlled trial (R01NR01691) ?Cognitive Behavioral Therapy for Insomnia: A Self-Management Strategy for Chronic Illness in Stable Heart Failure. Wrist actigraph measures of sleep characteristics, sleep and symptom diaries, psychomotor vigilance and 6-minute walk test distance, and self-report measures of insomnia, sleep, symptoms, and functional performance are obtained at baseline and follow-up and will be available for this supplement. We added measures of cognitive function to the parent study. The PROMIS cognitive abilities scale and the Psychomotor Vigilance Test (PVT) will be used as measures of cognitive function, and these data are collected in the ongoing study. Additional analyses for the supplement will include detailed parametric and non-parametric analyses of 24-hour actigraphic time series data (200 participants X 5 data collection points X 2 weeks of continuous data) to compute RARs and diurnal variation in light levels. Statistical methods will include time-series assessment of parametric and non-parametric RAR and cross- sectional and longitudinal multivariate methods. All analyses will statistically control for relevant covariates that may include changes in HF severity, comorbidity, baseline cognitive function, anxiety, depression, and treatment group (CBT-I vs. HF Self-management education ? control group), among others as they are identified in bivariate analyses.